I try to wrap the end around the beginning on circles. I don't start stitching at the beginning but an inch or two down the bias, then I fold over the end and wrap it around. They're far from perfect but not too bad. Does that make sense?

I just did my first circle and I folded on end under and stitched the inside of the circle and then when I got close to the end, I tucked it back under and made sure the folds butted together. I whip stitched the folded ends together. It's a bit thicker, but when I put it on the wall, you don't notice it. I also trimmed down the bias stem a bit on the part I turned under to reduce the bulk a tiny bit.